feat: add keyboard shortcuts to browser extension for ruler and mask

[jonahhb]

Added keyboard shortcuts that activate/deactivate the mask and ruler on browser extensions as requested in #44.

The shortcuts are: Ruler: CTRL+ALT+R Mask: CTRL+ALT+N (not m because of a conflict)

I have tested the functionality on Chrome and Firefox and it works as expected. I do not own a Mac to test Safari. All tests pass locally and in GitHub Actions. I did not contribute to any linter warnings.